Base station apparatus, and method for controlling transmission power for retransmitted packets

ABSTRACT

When an H-ARQ is used for downlink high-speed packet transmission, appropriate transmit power control is performed on a retransmission packet for effective use of transmit power resources and reduced interference in a radio communication system, and the transmit power of the retransmission packets (transmission # 2,  transmission # 3 ) is controlled to transmit power value so that the reception quality of the retransmission packets at the mobile station apparatus is lower than the reception quality of the initial transmission packet (transmission # 1 ) at the mobile station apparatus. For example, the transmit power value of the retransmission packet is controlled to a value lower than the transmit power value of the initial transmission packet by a predetermined value X [dB].

TECHNICAL FIELD

The present invention relates to a base station apparatus and a methodof controlling transmit power of a retransmission packet used in a radiocommunication system which carries out downlink high-speed packettransmission.

BACKGROUND ART

In the field of radio communications, a downlink high-speed packettransmission scheme has been developed in which a high-speed, largevolume downlink channel is shared by a plurality of mobile stationapparatuses and packets are transmitted from a base station apparatus tothe mobile station apparatuses. The downlink high-speed packettransmission scheme uses a scheduling technology and adaptive modulationtechnology to enhance transmission efficiency.

The scheduling technology is a technology whereby a base stationapparatus sets mobile station apparatuses to which downlink high-speedpackets are transmitted slot by slot and assigns packets to betransmitted to the respective mobile station apparatuses. On the otherhand, the adaptive modulation technology is a technology whereby amodulation scheme or error correcting coding scheme (MCS: Modulation andCoding Scheme) is adaptively determined according to the condition of apropagation path of a mobile station apparatus to which a packet istransmitted.

Furthermore, a radio communication system which carries out high-speedpacket transmission uses an ARQ (Automatic Repeat Request), and H-ARQ(Hybrid-Automatic Repeat Request) in particular, to improve the datareception performance.

In the ARQ, a base station apparatus and a mobile station apparatus areconnected through a bidirectional transmission path, the base stationapparatus transmits the mobile station apparatus a packet including acodeword generated by applying error detection coding to an informationbit to detect errors at the mobile station apparatus. When no error isdetected in the received packet, the mobile station apparatus transmitsa reception confirmation signal (Positive Acknowledgment: ACK signal)indicating that the packet has been received correctly and when an erroris detected in the received packet, the mobile station apparatustransmits a retransmission request signal (Negative Acknowledgment: NACKsignal) to the base station apparatus. Upon reception of a NACK signal,the base station apparatus retransmits the same packet. The base stationapparatus repeats retransmission of the same packet until an ACK signalis received.

For example, when the base station apparatus transmits a first packetand the mobile station apparatus receives this first packet correctly,the mobile station apparatus transmits an ACK signal to the base stationapparatus. Upon reception of this ACK signal, the base station apparatustransmits a second packet next. When this second packet is received withan error, the mobile station apparatus transmits a NACK signal to thebase station apparatus. When the base station apparatus receives theNACK signal from this mobile station apparatus, the base stationapparatus transmits the second packet again. That is, the base stationapparatus retransmits the same packet unless an ACK signal is receivedfrom the mobile station apparatus. In this way, the ARQ realizeshigh-quality transmission.

The above described ARQ can realize high-quality transmission, butpropagation delay may increase when retransmission is repeated.Especially when a propagation environment is poor, the data error rateincreases, and therefore the retransmission count increases and thepropagation delay increases drastically. As a technology of handlingpropagation delays in this ARQ, an H-ARQ is used in a radiocommunication system which carries out high-speed packet transmission.

The H-ARQ is a scheme combining the ARQ with an error correcting codeand is intended to improve the error rate of a received signal usingerror correction, reduce a retransmission count and thereby improvethroughput. As predominant schemes of this H-ARQ, two schemes areproposed; Chase Combining type and Incremental Redundancy type.

The Chase Combining type H-ARQ (hereinafter referred to as “CC typeH-ARQ”) is characterized in that a base station apparatus retransmitsthe same packet as that transmitted previously. Upon reception of theretransmitted packet, the mobile station apparatus combines thepreviously transmitted packet with the packet retransmitted this timeand carries out error correcting decoding on the combined signal. Inthis way, the CC type H-ARQ improves the reception level by combiningthe codeword included in the previously received packet and the codewordincluded in the packet retransmitted this time, and therefore the errorrate characteristic is improved every time retransmission is repeated.Thus, errors are eliminated at a smaller retransmission count than thenormal ARQ, and so throughput can be improved.

On the other hand, the Incremental Redundancy type H-ARQ (hereinafterreferred to as “IR type H-ARQ”) is characterized in that a base stationapparatus retransmits a packet including a parity bit different from aparity bit included in a previously transmitted packet. The mobilestation apparatus stores received parity bits in a buffer and when aretransmission packet is received, the mobile station apparatus performserror correcting decoding using both the parity bit included in thepreviously received packet and the parity bit included in the packetreceived at the time of retransmission. Thus, in the IR type, the paritybit used for error correcting decoding is incremented for eachretransmission, and therefore the error correction performance of themobile station apparatus improves and as a result, the error ratecharacteristic is improved every time retransmission is repeated. Inthis way, errors are eliminated at a smaller retransmission count thanthat in a normal ARQ, and so throughput can be improved.

In this H-ARQ, retransmission packets are used in an auxiliary mannerfor an initial transmission packet to improve the error ratecharacteristic.

Operations of the base station apparatus and mobile station apparatus inthe radio communication system which carries out high-speed packettransmission will be summarized below.

The base station apparatus predicts channel quality based on a reportedvalue of a downlink channel condition transmitted from each mobilestation apparatus, etermines the mobile station apparatus having thebest channel quality as the transmission destination and assigns apacket to each time slot for the destination. Then, the base stationapparatus carries out error correcting coding and modulation on thepacket based on the information indicating the scheduling result andaccording to the scheme determined by the scheduling, and transmits thepacket to the mobile station apparatus which becomes the transmissiondestination.

Each mobile station apparatus performs demodulation at a time slot towhich a packet directed to the mobile station apparatus is assignedbased on the received information indicating the scheduling result,performs CRC detection, etc., and when the packet data has beensuccessfully demodulated, the mobile station apparatus transmits an ACKsignal indicating the successful demodulation. On the other hand, whenthe packet data contains an error and the packet data has not beendemodulated correctly, each mobile station apparatus transmits a NACKsignal indicating the demodulation failure to the base station apparatusand thereby requests retransmission of the packet data.

Upon reception of an ACK signal, the base station apparatus transmitsthe next packet and upon reception of a NACK signal, the base stationapparatus retransmits the same packet.

Thus, according to the downlink high-speed packet transmission scheme,one channel is shared by all mobile station apparatuses existing in acell or sector and packets are transmitted efficiently, and thereby coderesources can be effectively used.

Now, when adaptive modulation and H-ARQ are used for down linkhigh-speed packet transmission, a technology for optimizing an MCSaccording to reception quality (e.g. Ec/N0, SIR, CIR, etc.) of a packetreceived at a mobile station apparatus is disclosed in, for example,Document “Comparison of Hybrid ARQ Packet Combining Algorithm in HighSpeed Downlink Packet Access in a Multipath Fading Channel, IEICE TRANS.FUNDAMENTALS, VOL.E85-A, NO.7, JULY 2002, pp.1557-1568.” According tothis document, transmit power of a downlink packet is supposed to bealways constant irrespective of whether it corresponds to the time ofinitial transmission or the time of retransmission as shown in FIG. 1.

As described above, the H-ARQ uses a retransmission packet as asupplement for an initial transmission packet to improve the error ratecharacteristic, and therefore the mobile station apparatus is notrequired to have so high reception quality at the time of retransmissionas at the time of initial transmission. Nonetheless, if transmit powerof a downlink packet is always constant irrespective of whether itcorresponds to the time of initial transmission or the time ofretransmission as in the case of the above described document, extratransmit power is used at the time of retransmission, which is notappropriate from the standpoint of effective use of transmit powerresources.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a base stationapparatus and a method of controlling transmit power of retransmissionpackets, when an H-ARQ is used for downlink high-speed packettransmission, capable of performing appropriate transmit power controlover retransmission packets to effectively use transmit power resourcesand reducing interference in a radio communication system.

In order to attain the above described object, according to the presentinvention, a base station apparatus controls transmit power of aretransmission packet to a transmit power value so that receptionquality of the retransmission packet at a mobile station apparatus islower than reception quality of the initial transmission packet at themobile station apparatus. This allows transmit power resources to beeffectively used and interference in the radio communication system tobe decreased.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates conventional transmit power;

FIG. 2 is a block diagram showing a configuration of a base stationapparatus according to Embodiment 1 of the present invention;

FIG. 3 illustrates a block diagram showing a configuration of a mobilestation apparatus according to Embodiment 1 of the present invention;

FIG. 4 is a block diagram showing a configuration of a scheduler of thebase station apparatus according to Embodiment 1 of the presentinvention;

FIG. 5 illustrates transmit power control according to Embodiment 1 ofthe present invention;

FIG. 6 illustrates transmit power control according to Embodiment 2 ofthe present invention;

FIG. 7 is a block diagram showing a configuration of a scheduler of abase station apparatus according to Embodiment 3 of the presentinvention;

FIG. 8 illustrates a change in quality of a downlink channel accordingto Embodiment 3 of the present invention;

FIG. 9 illustrates transmit power control according to Embodiment 3 ofthe present invention;

FIG. 10 illustrates reception power according to Embodiment 3 of thepresent invention;

FIG. 1 is block diagram showing a configuration of a scheduler of a basestation apparatus according to Embodiment 4 of the present invention;

FIG. 12 is a graph illustrating a relationship between an SIR and FER(Frame Error Rate) per transmission when a modulation scheme accordingto Embodiment 4 of the present invention is QPSK;

FIG. 13 is a table illustrating correspondence between a retransmissioncount and IR gain according to Embodiment 4 of the present invention;

FIG. 14 illustrates transmit power control according to Embodiment 4 ofthe present invention;

FIG. 15 is a block diagram showing a configuration of a scheduler of abase station apparatus according to Embodiment 5 of the presentinvention;

FIG. 16 illustrates transmit power control according to Embodiment 5 ofthe present invention;

FIG. 17 illustrates reception power according to Embodiment 5 of thepresent invention;

FIG. 18 is a block diagram showing a configuration of a scheduler of abase station apparatus according to Embodiment 6 of the presentinvention;

FIG. 19A illustrates transmit power control according to Embodiment 6 ofthe present invention;

FIG. 19B illustrates transmit power control according to Embodiment 6 ofthe present invention;

FIG. 19C illustrates transmit power control according to Embodiment 6 ofthe present invention; and

FIG. 19D illustrates transmit power control according to Embodiment 6 ofthe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference now to the attached drawings, embodiments of the presentinvention will be explained in detail below. In the followingexplanations, suppose an HSDPA (High Speed Downlink Packet Access) willbe used as an example of a downlink high-speed packet transmissionscheme. The HSDPA uses a plurality of channels such as HS-PDSCH (HighSpeed—Physical Downlink Shared Channel), HS-SCCH (Shared Control Channelof HS-PDSCH), A-DPCH (Associated-Dedicated Physical Channel forHS-PDSCH) and HS-DPCCH (High Speed—Dedicated Physical Control Channel).

The HS-PDSCH is a shared channel in a downlink used for transmission ofpackets. The HS-SCCH is a shared channel in a downlink and transmitsinformation on resource assignment (TFRI: Transport-format and Resourcerelated Information) and information on H-ARQ control, etc.

The A-DPCH is a dedicated associated channel in uplink and downlink andhas the same channel configuration and handover control, etc., as thoseof the DPCH. The A-DPCH transmits pilot signals and TPC commands, etc.The HS-DPCCH in an uplink transmit an ACK/NACK signal and CQI (ChannelQuality Indicator) signal. The CQI signal is a signal indicating amodulation scheme and a coding rate of packet data which can bedemodulated at a mobile station apparatus and plays a role of a reportvalue for reporting a downlink channel condition.

Embodiment 1

FIG. 2 is a block diagram showing a configuration of a base stationapparatus according to Embodiment 1 of the present invention. Variouscomponents of a base station apparatus 100 in FIG. 2 will be explainedbelow.

A duplexer 102 outputs a signal received by an antenna 101 to areception RF section 103. Furthermore, the duplexer 102 transmits asignal output from a transmission RF section 166 from the antenna 101 byradio.

The reception RF section 103 converts the received signal of a radiofrequency output from the duplexer 102 to a baseband digital signal andoutputs the signal to a demodulation section 104.

There are as many demodulation sections 104 as mobile stationapparatuses with which radio communications are carried out, forperforming demodulation processing such as despreading, RAKE combining,error correcting decoding on the received baseband signal and outputtingthe signal to a separation section 105.

The separation section 105 separates the output signal of thedemodulation section 104 into data and a control signal. The controlsignal separated by the separation section 105 includes DL (Down Link)TPC command, CQI signal and ACK/NACK signal, etc. The CQI signal andACK/NACK signal are output to a scheduler 151, while the DL TPC commandis output to a transmit power control section 158.

There are as many SIR measuring sections 106 as mobile stationapparatuses with which radio communications are carried out, formeasuring a reception SIR on an uplink according to a desired signallevel and interference signal level measured in the process ofdemodulation and outputs a signal indicating the SIR to a TPC commandgeneration section 107.

There are as many TPC command generation sections 107 as mobile stationapparatuses with which radio communications are carried out, forgenerating a UL (Up Link) TPC command which instructs anincrease/decrease of uplink transmit power according to a magnituderelationship between the reception SIR on the uplink and a target SIR.

The scheduler 151 determines a mobile station apparatus to which apacket is transmitted based on a packet transmission control signal, CQIsignal from each mobile station apparatus and ACK/NACK signal andoutputs information indicating the mobile station apparatus and packetdata to be transmitted to a buffer (Queue) 152. Furthermore, thescheduler 151 determines a modulation scheme, coding rate and codemultiplexing number based on the CQI signal from the mobile stationapparatus and instructs a modulation section 153 on them. Furthermore,the scheduler 151 determines transmit power of packet data based on theACK/NACK signal from the mobile station apparatus and outputs a signalindicating the transmit power to a transmit power control section 154.Furthermore, the scheduler 151 outputs a signal (hereinafter referred toas “HS-SCCH signal”) to be transmitted to the mobile station apparatususing an HS-SCCH to an amplification section 161. The HS-SCCH signalincludes information (TFRI) on a timing for transmitting packet data,coding rate and modulation scheme of the packet data, etc. Theconfiguration of the scheduler 151 will be explained later.

The buffer 152 outputs the packet data for the mobile station apparatusinstructed by the scheduler 151 to the modulation section 153.

The modulation section 153 performs error correcting coding, modulationand spreading on the packet data according to instructions of thescheduler 151 and outputs the packet data to an amplification section155.

The transmit power control section 154 controls an amount ofamplification of the amplification section 155 to thereby control thetransmit power of the output signal of the modulation section 153 to avalue determined by the scheduler 151. The output signal of theamplification section 155 is a signal transmitted using an HS-PDSCH andoutput to a multiplexing section 165.

There are as many multiplexing sections 156 as mobile stationapparatuses with which radio communications are carried out, formultiplexing pilot signals and UL TPC commands with dedicated data (alsoincluding control signals) to be transmitted to each mobile stationapparatus and outputting the multiplexed signal to a modulation section157.

There are as many modulation sections 157 as mobile station apparatuseswith which radio communications are carried out, for carrying out errorcorrecting coding, modulation and spreading on the output signal of themultiplexing section 156 and outputting the signal to an amplificationsection 159.

There are as many transmit power control sections 158 as mobile stationapparatuses with which radio communications are carried out, forcontrolling transmit power of the output signal of the modulationsection 157 by controlling the amount of amplification of theamplification section 159 according to a DL TPC command. Furthermore,the transmit power control section 158 outputs a signal indicating atransmit power value to a transmit power control section 160. The signalamplified by the amplification section 159 is a signal transmitted usinga DPCH (including A-DPCH) and output to the multiplexing section 165.

The transmit power control section 160 controls transmit power of anHS-SCCH signal output from the scheduler 151 by controlling the amountof amplification of the amplification section 161 with a value obtainedby adding an offset to the transmit power value of the transmit powercontrol section 158. The signal amplified by the amplification section161 is a signal transmitted using an HS-SCCH and output to themultiplexing section 165. The transmit power control section 160 mayalso correct the offset value according to a retransmission condition,etc.

A modulation section 162 carries out error correcting coding, modulationand spreading on common control data and outputs the control data to anamplification section 164. A transmit power control section 163 controlstransmit power of the output signal of the modulation section 162 bycontrolling the amount of amplification of the amplification section164. The output signal of the amplification section 164 is a signaltransmitted using a CPICH, etc., and output to the multiplexing section165.

The multiplexing section 165 multiplexes the output signals of theamplification section 155, amplification section 159, amplificationsection 161 and amplification section 164 and outputs the multiplexedsignal to a transmission RF section 166.

The transmission RF section 166 converts the baseband digital signaloutput from the modulation section 159 to a signal with a radiofrequency and outputs the signal to the duplexer 102.

FIG. 3 is a block diagram showing a configuration of a mobile stationapparatus which carries out radio communications with the base stationapparatus shown in FIG. 2. A mobile station apparatus 200 in FIG. 3receives dedicated data, common control data, packet data and HS-SCCHsignal from the base station apparatus 100. Various components of themobile station apparatus 200 in FIG. 3 will be explained below.

A duplexer 202 outputs the signal received by an antenna 201 to areception RF section 203. The duplexer 202 also transmits a signaloutput from a transmission RF section 258 from the antenna 201 by radio.

The reception RF section 203 converts the received signal with the radiofrequency output from the duplexer 202 to a baseband digital signal andoutputs an HS-PDSCH signal to a buffer 204, outputs an HS-SCCH signal toa demodulation section 205, outputs a DPCH signal to a demodulationsection 208 and outputs a shared control channel signal to a CIR(Carrier to Interference Ratio) measuring section 212.

The buffer 204 temporarily stores the HS-PDSCH signal and outputs thesignal to a demodulation section 206.

The demodulation section 205 carries out demodulation processing such asdespreading, RAKE combining and error correcting decoding on the HS-SCCHsignal, acquires information necessary for demodulation of packet datasuch as an arrival timing of packet data directed to the mobile stationapparatus 200, coding rate and modulation scheme of the packet data andoutputs the information to the demodulation section 206.

The demodulation section 206 carries out demodulation processing such asdespreading, RAKE combining and error correcting decoding on theHS-PDSCH signal stored in the buffer based on the information acquiredby the demodulation section 205 and outputs the packet data obtainedthrough demodulation processing to the error detection section 207.

An error detection section 207 carries out error detection on the packetdata output from the demodulation section 206 and outputs an ACK signalwhen no error is detected and a NACK signal when an error is detected toa multiplexing section 251.

The demodulation section 208 carries out demodulation processing such asdespreading, RAKE combining and error correcting decoding on the DPCHsignal and outputs the DPCH signal to a separation section 209.

The separation section 209 separates the output signal of thedemodulation section 208 into data and a control signal. The controlsignal separated by the separation section 209 includes a UL TPCcommand, etc. The UL TPC command is output to a transmit power controlsection 257.

An SIR measuring section 210 measures a reception SIR of the downlinkaccording to a desired signal level and interference signal levelmeasured in the process of demodulation and outputs all the measuredreception SIRs to a TPC command generation section 211.

The TPC command generation section 211 generates a DL TPC commandaccording to a magnitude relationship between the reception SIR outputfrom the SIR measuring section 210 and a target SIR and outputs the DLTPC command to a multiplexing section 254.

The CIR measuring section 212 measures a CIR using the common controlchannel signal from the base station apparatus and outputs themeasurement result to a CQI generation section 213. The CQI generationsection 213 generates a CQI signal based on the CIR of the signaltransmitted from the base station apparatus and outputs the CQI signalto the multiplexing section 251.

The multiplexing section 251 multiplexes the CQI signal and ACK/NACKsignal and outputs the multiplexed signal to a modulation section 252.The modulation section 252 carries out error correcting coding,modulation and spreading on the output signal of the multiplexingsection 251 and outputs the signal to a multiplexing section 256.

A modulation section 253 carries out error correcting coding, modulationand spreading on the data to be transmitted to the base stationapparatus 100 and outputs the data to the multiplexing section 256.

The multiplexing section 254 multiplexes a DL TPC command and pilotsignal and outputs the multiplexed signal to a modulation section 255.The modulation section 255 carries out error correcting coding,modulation and spreading on the output signal of the multiplexingsection 254 and outputs the output signal to the multiplexing section256.

The multiplexing section 256 multiplexes the output signals of themodulation section 252, modulation section 253 and modulation section255 and outputs the multiplexed signal to the transmission RF section258.

The transmit power control section 257 controls transmit power of theoutput signal of the multiplexing section 256 by controlling an amountof amplification of the transmission RF section 258 according to a ULTPC command. When the mobile station is connected to a plurality of basestation apparatuses, the transmit power control section 257 performscontrol for increasing transmit power only when all UL TPC commandsinstruct an increase of transmit power.

The transmission RF section 258 amplifies the baseband digital signaloutput from the multiplexing section 256, converts the baseband digitalsignal to a signal with a radio frequency and outputs the signal to theduplexer 102.

Next, the configuration of the scheduler 151 of the base stationapparatus 100 will be explained using FIG. 4.

The scheduler 151 is mainly constructed of a transmission destinationdetermining section 301, an MCS determining section 302, a transmitpower determining section 303 and an HS-SCCH signal generation section304.

The transmission destination determining section 301 selects each mobilestation apparatus which becomes a candidate to which a packet istransmitted, using a packet transmission control signal and determines amobile station apparatus to which a packet is transmitted based on theCQI signal from the selected mobile station apparatus. For example, amobile station apparatus having the best reception quality is determinedas the packet transmission destination based on the CQI signal. Then,the transmission destination determining section 301 outputs informationindicating the mobile station apparatus designated as the destination tothe buffer 152, MCS determining section 302 and HS-SCCH signalgeneration section 304. The transmission destination determining section301 instructs the buffer 152 to transmit a new packet when an ACK signalis received and to retransmit the previously transmitted packet when anNACK signal is received.

The MCS determining section 302 selects an MCS (determines themodulation scheme, coding rate and code multiplexing number) based onthe CQI signal of the mobile station apparatus, instructs the modulationsection 153 on the MCS and inputs the MCS to the HS-SCCH signalgeneration section 304.

The transmit power determining section 303 applies different transmitpowers of a packet between when an ACK signal is received and when aNACK signal is received from the mobile station apparatus, and lowersthe reception quality (e.g., Ec/N0, SIR, CIR, etc.) of a retransmissionpacket at the mobile station apparatus than the reception quality of aninitial transmission packet. More specifically, when an ACK signal isreceived, the transmit power determining section 303 determines thetransmit power of the initial transmission packet (transmission #1) tobe transmitted next to a predetermined value P(1) [dB] as shown in FIG.5. On the other hand, when a NACK signal is received in response to theinitial transmission packet (transmission #1), the transmit power of thefirst retransmission packet (transmission #2) is set to a value lowerthan the transmit power P(1) [dB] of the initial transmission packet(transmission #1) by a predetermined value X [dB] as shown in FIG. 5.Furthermore, when another NACK signal is received in response to thefirst retransmission packet (transmission #2), the transmit power of thesecond retransmission packet (transmission #3) is also set to a valuelower than the transmit power P(1) [dB] of the initial transmissionpacket (transmission #1) by the predetermined value X [dB] as shown inFIG. 5. That is, the transmit power of both the first retransmissionpacket (transmission #2) and second retransmission packet (transmission#3) is set to the value lower than the transmit power P(1) [dB] of theinitial transmission packet (transmission #1) by the predetermined valueX [dB]. In this way, the transmit power determining section 303 sets thetransmit power of a retransmission packet for an HS-PDSCH to a valuelower than the transmit power of an initial transmission packet for anHS-PDSCH, and thereby lowers the reception quality of the retransmissionpacket at the mobile station apparatus compared to the reception qualityof the initial transmission packet. Then, the transmit power determiningsection 303 outputs a signal indicating the determined transmit power tothe transmit power control section 154. Following this indication, thetransmit power control section 154 controls the transmit power of theretransmission packet to a value lower than the transmit power of theinitial transmission packet by X [dB].

The HS-SCCH signal generation section 304 generates an HS-SCCH signalfor the mobile station apparatus including the MCS selected by the MCSdetermining section 302 and outputs the HS-SCCH signal to theamplification section 161.

Thus, according to this embodiment, the transmit power of aretransmission packet is lowered compared to the transmit power of aninitial transmission packet, and the reception quality of theretransmission packet at the mobile station apparatus is lower than thereception quality of the initial transmission packet, and therefore itis possible to reduce interference in the radio communication system andsave the consumption of transmit power resources. Furthermore, themobile station apparatus has already successfully received a certaindegree of necessary data through the initial transmission packet, andcan thereby improve the error rate characteristic by carrying out anH-ARQ even if the reception quality of a retransmission packet is lower.That is, the mobile station apparatus which carries out an H-ARQ uses aretransmission packet as a supplement to an initial transmission packet,and therefore the degradation of reception quality of the retransmissionpacket constitutes no particular problem in improving the error ratecharacteristic.

Embodiment 2

With an H-ARQ, the degree of contribution of a retransmission packet toimprovement of an error rate decreases as a retransmission countincreases. That is, reception quality of a retransmission packet at amobile station apparatus required for a second retransmission is lowerthan that for a first retransmission. Therefore, the base stationapparatus according to this embodiment changes the width of reduction oftransmit power of a retransmission packet with respect to an initialtransmission packet according to a retransmission count. That is,transmit power is decreased as the retransmission count increases.

In the base station apparatus according to this embodiment, uponreception of an ACK signal, the transmit power determining section 303shown in FIG. 4 determines the transmit power of an initial transmissionpacket (transmission #1) to be transmitted next to a predetermined valueP(1) [dB] as shown in FIG. 6. On the other hand, upon reception of aNACK signal in response to the initial transmission packet (transmission#1), the transmit power determining section 303 determines the transmitpower of the first retransmission packet (transmission #2) to a valuelower than the transmit power P(1) [dB] of the initial transmissionpacket (transmission #1) by a predetermined value X(2) [dB] as shown inFIG. 6. Furthermore, when a further NACK signal is received in responseto the first retransmission packet (transmission #2), the transmit powerof the second retransmission packet (transmission #3) is set to a valuelower than the transmit power P(1) [dB] of the initial transmissionpacket (transmission #1) by a predetermined value X(3) [dB] (>X(1) [dB])as shown in FIG. 5. That is, the transmit power of a retransmissionpacket is decreased gradually as the retransmission count increases.

In this way, by gradually decreasing the transmit power of aretransmission packet as the retransmission count increases, it ispossible to further decrease interference in the radio communicationsystem and further save consumption of transmit power resources.

Embodiment 3

This embodiment will explain a case where transmit power control isperformed on a retransmission packet with consideration given to avariation in a downlink channel condition. FIG. 7 is a block diagramshowing a configuration of a scheduler of a base station apparatusaccording to this embodiment and has a configuration with a CQIdifference calculation section 305 added to the configuration in FIG. 4.

A CQI difference calculation section 305 calculates a difference betweena CQI value at the time of initial transmission and a CQI value at thetime of retransmission based on the input CQI signals and inputs thisCQI value difference to a transmit power determining section 303. Thetransmit power determining section 303 determines transmit power of aretransmission packet using the input CQI value difference.

Since the mobile station apparatus transmits a CQI signal correspondingto a combination of the modulation scheme and coding rate determinedaccording to the downlink channel quality to the base station apparatus,the CQI signal can be said to indicate downlink channel quality.Furthermore, the CQI signal is expressed with a CQI value from ‘1’ to‘30’ according to the downlink channel quality, which indicates that thedownlink channel quality improves as the value increases. Furthermore,the CQI value difference is substantially the same as the difference indB units. Therefore, when the CQI difference calculation section 305calculates the difference between a CQI value at the time of initialtransmission and a CQI value at the time of retransmission, it ispossible to calculate the difference between the downlink channelquality at the time of initial transmission packet transmission and thedownlink channel quality at the time of retransmission packettransmission in dB units.

This will be explained more specifically using FIG. 8 to FIG. 10.

First, as shown in FIG. 8, the CQI difference calculation section 305calculates a difference between a CQI value at the time of initialtransmission and a CQI value at the time of retransmission. That is, adifference CQI_d(2) between CQI(1) which is the CQI value of the initialtransmission packet (transmission #1) and CQI(2) which is the CQI valueof the first retransmission packet (transmission #2) is calculated fromthe following Expression (1):CQI_d(2)=CQI(1)−CQI(2)   (1)

Here, the downlink channel quality at the time of first retransmission(transmission #2) is worse than that at the time of initial transmission(transmission #1), and therefore CQI(2) has a value smaller than that ofCQI(l) and CQI_d(2) results in a positive value.

Likewise, a difference CQI_d(3) between CQI(1) which is the CQI value ofthe initial transmission packet (transmission #1) and CQI(3) which isthe CQI value of the second retransmission packet (transmission #3) iscalculated from the following Expression (2):CQI_d(3)=CQI(1)−CQI(3)   (2)

Here, the downlink channel quality at the time of second retransmission(transmission #3) is better than the downlink channel quality at thetime of initial transmission (transmission #1), and therefore CQI (3)has a greater value than CQI(1) and CQI_d(3) results in a negativevalue.

Then, the transmit power determining section 303 determines transmitpower of a retransmission packet as shown in FIG. 9 according to the CQIvalue difference calculated by the CQI difference calculation section305. That is, if the transmit power at the time of initial transmission(transmission #1) is P(1) [dB] , the transmit power value P(2) of thefirst retransmission packet (transmission #2) is given by the followingExpression (3) and the transmit power value P(3) of the secondretransmission packet (transmission #3) is given by the followingExpression (4). X [dB] in Expressions (3) and (4) is the same as thepredetermined value X [dB] explained in Embodiment 1.P(2)=P(1)−X+CQI_d(2)   (3)P(3)=P(1)−X+CQI_d(3)   (4)

Since the transmit power determining section 303 determines the transmitpower of a retransmission packet according to the CQI value differencebetween initial transmission and retransmission as shown in Expressions(3) and (4), that is, the difference between the downlink channelquality at the time of initial transmission packet transmission and thedownlink channel quality at the time of retransmission packettransmission, even if the downlink channel quality changes between thetime of initial transmission and the time of retransmission, as shown inFIG. 10, reception power (reception quality) of a retransmission packetat the mobile station apparatus in the HS-PDSCH always has a value lowerthan the reception power (reception quality) of the initial transmissionpacket by a predetermined value X [dB].

In this way, according to this embodiment, even if the downlink channelquality changes between the time of initial transmission and the time ofretransmission, the transmit power of a retransmission packet isdetermined with consideration given to the change in the downlinkchannel quality, and therefore it is possible to always keep thereception quality of the retransmission packet at the mobile stationapparatus lower than the reception quality of the initial transmissionpacket by a predetermined value.

Embodiment 4

This embodiment will explain a case where an IR type H-ARQ is used asthe H-ARQ and transmit power of a retransmission packet is lowered bythe proportion of the gain of the IR type H-ARQ over the CC type H-ARQ.

FIG. 11 is a block diagram showing a configuration of a scheduler of abase station apparatus according to this embodiment and adopts aconfiguration with an IR gain determining section 306 added to theconfiguration in FIG. 4.

The IR gain determining section 306 receives a signal indicating amodulation scheme determined by an MCS determining section 302.Furthermore, the IR gain determining section 306 receives an ACK/NACKsignal. When a NACK signal is input (that is, in the case ofretransmission), the IR gain determining section 306 calculates a gain(IR gain) of the IR type H-ARQ over the CC type H-ARQ and inputs asignal indicating the IR gain to a transmit power determining section303. The transmit power determining section 303 determines transmitpower of a retransmission packet using the input IR gain.

This will be explained more specifically using FIG. 12 to FIG. 14 below.

First, the IR gain will be explained. FIG. 12 is a graph showing arelationship between an SIR and FER (Frame Error Rate) per transmissionwhen the modulation scheme is QPSK. This graph shows a reception SIRobtained when transmission is performed only once (1 Tx) and receptionSIR obtained per transmission when transmission is performed twice withthe same power (2 Tx). Since an H-ARQ is performed here, performingtransmission twice (2 Tx) can reduce a required reception SIR pertransmission at a mobile station apparatus compared to performingtransmission only once (1 Tx). Furthermore, the SIR of the IR type H-ARQcan be further reduced compared to the SIR of the CC type H-ARQ and thedifference in these SIRs is an IR gain. This IR gain increases as theretransmission count increases. However, as the retransmission countincreases, the coding rate at the mobile station apparatus graduallydecreases and the IR gain becomes substantially constant after all codedbits of systematic bits and parity bits are received by the mobilestation apparatus. The IR gain is obtained not only in a coding scheme(turbo coding) in which coded bits are divided into systematic bits andparity bits but also in convolutional coding, etc.

Based on the graph shown in FIG. 12, the IR gain determining section 306sets a table as shown in FIG. 13 showing the correspondence between aretransmission count and IR gain for each modulation scheme and the IRgain determining section 306 determines an IR gain according to aretransmission count with reference to this table. For example, when themodulation scheme determined y the MCS determining section 302 is QPSKand in the case of a first retransmission packet (transmission #2), theIR gain is determined as Y(2)=2 [dB]. Furthermore, when the modulationscheme determined by the MCS determining section 302 is QPSK and in thecase of a second retransmission packet (transmission #3), the IR gain isdetermined as Y(3)=4 [dB]. In the table shown in FIG. 13, the IR gainremains constant after the third retransmission packet (transmission#4).

Then, the transmit power determining section 303 determines transmitpower of a retransmission packet as shown FIG. 14 according to the IRgain calculated by the IR gain determining section 306. That is, when aNACK signal is received in response to an initial transmission packet(transmission #1), the transmit power of the first retransmission packet(transmission #2) is determined as a value lower than the transmit powerP(1) [dB] of the initial transmission packet (transmission #1) by Y(2)=2[dB] as shown in FIG. 14. Furthermore, when a NACK signal is received inresponse to the first retransmission packet (transmission #2), thetransmit power of the second retransmission packet (transmission #3) isdetermined as a value lower than the transmit power P(1) [dB] of theinitial transmission packet (transmission #1) by Y(3)=4 [dB] as shown inFIG. 14. In this way, as the retransmission count increases, the IR gainincreases, and therefore transmit power of a retransmission packetgradually decreases. However, in the table shown in FIG. 13, the IR gainremains constant after the third retransmission packet (transmission#4), and therefore transmit power becomes constant after the thirdretransmission packet.

Thus, according to this embodiment, the amount of decrease of transmitpower of a retransmission packet corresponds to an IR gain correspondingto a retransmission count, and therefore when an IR type H-ARQ is usedas the H-ARQ, it is possible to keep reception quality at the mobilestation apparatus to the reception quality higher than when a CC typeH-ARQ is used, decrease interference in a radio communication system andsave the consumption of transmit power resources.

Embodiment 5

This embodiment will explain a case where an IR type H-ARQ is used asthe H-ARQ and transmit power of a retransmission packet is controlled inconsideration of a variation in the downlink channel condition. FIG. 15is a block diagram showing a configuration of a scheduler of a basestation apparatus according to this embodiment and adopts aconfiguration with a CQI difference calculation section 305 and IR gaindetermining section 306 added to the configuration in FIG. 4. The CQIdifference calculation section 305 shown in FIG. 15 is the same as theCQI difference calculation section 305 shown in FIG. 7 and the IR gaindetermining section 306 shown in FIG. 15 is the same as the IR gaindetermining section 306 shown in FIG. 11, and so explanations thereofwill be omitted here. According to this embodiment, the transmit powerdetermining section 303 determines transmit power of a retransmissionpacket using the CQI value difference calculated at the CQI differencecalculation section 305 and the IR gain determined by the IR gaindetermining section 306.

This will be explained more specifically using FIG. 16 and FIG. 17below.

As shown in FIG. 16, if the transmit power at the time of initialtransmission (transmission #1) is P(1) [dB], the transmit power valueP(2) of the first retransmission packet (transmission #2) is given bythe following Expression (5) and the transmit power value P(3) of thesecond retransmission packet (transmission #3) is given by the followingExpression (6). In the following Expressions (5) and (6), CQI_d(2) andCQI_d(3) are the same as CQI_d(2) and CQI_d(3) explained in Embodiment 3and Y(2) and Y(3) are the same as Y(2) and Y(3) explained in Embodiment4.P(2)=P(1)−Y(2)+CQI_d(2)   (5)P(3)=P(1)−Y(3)+CQI_d(3)   (6)

Since as shown in Expression (5) and (6), the transmit power determiningsection 303 determines the transmit power of a retransmission packetaccording to a difference in the CIQ value at the time of initialtransmission and at the time of retransmission (that is, differencebetween downlink channel quality at the time of initial transmissionpacket transmission and downlink channel quality at the time ofretransmission packet transmission) and the IR gain, when an IR typeH-ARQ is used as the H-ARQ, even if the downlink channel quality changesat the time of initial transmission and at the time of retransmission,the reception power (reception quality) of a retransmission packetdecreases as the retransmission count increases in the HS-PDSCH at themobile station apparatus as shown in FIG. 17.

Thus, according to this embodiment, when an IR type H-ARQ is used as theH-ARQ, even if the downlink channel quality changes at the time ofinitial transmission and at the time of retransmission, the transmitpower of a retransmission packet is determined in consideration of thechange in the downlink channel quality and IR gain, and therefore it ispossible to always keep the reception quality of a retransmission packetat the mobile station apparatus lower than the reception quality of aninitial transmission packet.

Embodiment 6

This embodiment will explain a case where extra transmit power resourcesproduced by reducing transmit power of a retransmission packet aredistributed to other packets. FIG. 18 is a block diagram showing aconfiguration of a scheduler of a base station apparatus according tothis embodiment and adopts a configuration with an IR gain determiningsection 306 added to the configuration in FIG. 4. The IR gaindetermining section 306 shown in FIG. 18 is the same as the IR gaindetermining section 306 shown in FIG. 11, and so explanations thereofwill be omitted.

In this embodiment, a transmit power determining section 303 determinestransmit power of a retransmission packet using an IR gain determined bythe IR gain determining section 306 and outputs a signal indicating thedetermined transmit power to a transmit power control section 154.Furthermore, the transmit power determining section 303 knows a totalamount (total transmit power) of transmit power resources beforehand,subtracts the determined transmit power from this total transmit powerto calculate an amount of extra transmit power resources (extra transmitpower). Then, the transmit power determining section 303 inputs a signalindicating the extra transmit power to a transmission destinationdetermining section 301.

The transmission destination determining section 301 determines onemobile station apparatus as the packet transmission destination, andthen adds other mobile station apparatuses as the packet transmissiondestinations when there is extra transmit power. That is, extra transmitpower is distributed to other packets to be transmitted to the othermobile station apparatuses. When there is extra transmit power, thiscauses a plurality of different packets for a plurality of mobilestation apparatuses to be code-multiplexed and transmittedsimultaneously.

Or after one mobile station apparatus is determined as the packettransmission destination, if there is extra transmit power, thetransmission destination determining section 301 increases the number ofpackets to be transmitted to the one mobile station apparatus. That is,the transmission destination determining section 301 distributes theextra transmit power to other packets to be transmitted to the samemobile station apparatus. In this way, when there is extra transmitpower, a plurality of different packets for the same mobile stationapparatus is code-multiplexed and transmitted simultaneously.

A case where extra transmit power is distributed to other packets to betransmitted to other mobile station apparatus will be explained as anexample more specifically using FIGS. 19A to 19D. Here, suppose thereare three mobile station apparatuses A to C. FIG. 19A shows transmitpower of an HS-PDSCH distributed to a mobile station apparatus A, FIG.19B shows transmit power of an HS-PDSCH distributed to a mobile stationapparatus B, FIG. 19C shows transmit power of an HS-PDSCH distributed toa mobile station apparatus C and FIG. 19D shows total transmit power ofan HS-PDSCH distributed to the mobile station apparatuses A to C. Here,the transmit power for the mobile station apparatus A is determined inthe same way as for Embodiment 4.

Suppose the mobile station apparatus A uses all of the total transmitpower at initial transmission (transmission #1) (FIG. 19A). Therefore,it is not possible to code-multiplex the other mobile stationapparatuses B, C at the initial transmission (transmission #1) (FIGS.19B to D).

Next, at a first retransmission (transmission #2), the transmit powerdistributed to the mobile station apparatus A is decreased by Y(2) fromthat at the time of initial transmission (FIG. 19A). That is, extratransmit power Y(2) is produced. This extra transmit power Y(2) isdistributed to the mobile station apparatus B (FIG. 19B). Therefore, atthe first retransmission (transmission #2), the packet to the mobilestation apparatus A and the packet to the mobile station apparatus B arecode-multiplexed and transmitted (FIG. 19D).

Next, at a second retransmission (transmission #3) the transmit power tobe distributed to the mobile station apparatus A is decreased from thatat the time of initial transmission by Y(3) (FIG. 19A) . That is, extratransmit power Y(3) is produced. This extra transmit power Y(3) isdistributed to the mobile station apparatus C (FIG. 19C) Therefore, atthe second retransmission (transmission #3), the packet to the mobilestation apparatus A and the packet to the mobile station apparatus C arecode-multiplexed and transmitted (FIG. 19D).

In this way, by distributing extra transmit power to other packets tothe other mobile station apparatuses, the total transmit power of anHS-PDSCH signal transmitted by the base station apparatus always becomesconstant (FIG. 19D). That is, according to this embodiment, it ispossible to effectively use transmit power resources. It is alsopossible to increase the code-multiplexing number of packets and therebyimprove throughput.

This embodiment uses Embodiment 3 to determine transmit power, but canalso use any one of Embodiments 1 to 5.

As described above, according to the present invention, when an H-ARQ isused for downlink high-speed packet transmission, it is possible toperform appropriate transmit power control over a retransmission packetto effectively use transmit power resources and reduce interference in aradio communication system.

This application is based on the Japanese Patent Application No.2002-337208 filed on Nov. 20, 2002, entire content of which is expresslyincorporated by reference herein.

1. A base station apparatus comprising: a transmit power determiningsection that, out of an initial transmission packet and a retransmissionpacket to be transmitted to a mobile station apparatus on a downlink, asets transmit power of the retransmission packet to a transmit powervalue so that a reception quality of the retransmission packet-at themobile station apparatus is lower than the reception quality of theinitial transmission packet at the mobile station apparatus; a controlsection that controls the transmit power of the retransmission packet tothe transmit power value set by said transmit power determining section;and a distribution section that distributes extra transmit power foundfrom the transmit power value set by said transmit power determiningsection and a total transmit power to a packet other than theretransmission packet.
 2. The base station apparatus according to claim1, wherein said transmit power determining section sets the transmitpower value of the retransmission packet to a value lower than thetransmit power value of the initial transmission packet.
 3. The basestation apparatus according to claim 2, wherein said transmit powerdetermining section sets the transmit power value of the retransmissionpacket to a lower value as a retransmission count increases.
 4. The basestation apparatus according to claim 1, further comprising a calculationsection that calculates a difference between downlink channel quality atthe time of the initial transmission packet transmission and downlinkchannel quality at the time of the retransmission packet transmission,wherein said transmit power determining section determines the transmitpower value of the retransmission packet according to the differencecalculated by said calculation section.
 5. The base station apparatusaccording to claim 1, further comprising a gain determining-section thatdetermines a gain of an IR type hybrid ARQ over a CC type hybrid ARQ,wherein said transmit power determining section determines the transmitpower value of the retransmission packet according to the gaindetermined by said gain determining section.
 6. (canceled)
 7. A methodof controlling transmit power of a retransmission packet comprising: atransmit power determining step of setting transmit power of aretransmission packet, out of an initial transmission packet and theretransmission packet to be transmitted to a mobile station apparatus ona downlink, to a transmit power value so that the reception quality ofthe retransmission packet at the mobile station apparatus is lower thanthe reception quality of the initial transmission packet at the mobilestation apparatus; a control step of controlling the transmit power ofthe retransmission packet to the transmit power value set in saidtransmit power determining step; and a distribution step of distributingextra transmit power found from the transmit power value set in saidtransmit power determining step and a total transmit power to a packetother than the retransmission packet.